Battery charging system

ABSTRACT

A generator battery charging system is disclosed in which a shunt load is periodically switched across the output of the generator during periods of low charging current requirements from the battery to provide a substantially constant load on the generator.

States Patent [1 1 BATTERY CHARGlNG SYSTEM Inventor: Charles W. Cox,Houston, Tex.

Assignee:

Tex.

June 14, 1972 Filed:

Appl. No.:

US. Cl 320/27, 320/39, 320/71, 322/28, 322/91, 322/98 Int. Cl. H02j 7/14Field of Search 322/20, 28, 91, 95, 322/96, 97, 98; 320/27, 39, 61, 71

References Cited UNITED STATES PATENTS Automatic Power, Inc., Houston,

Hill 322/91 X 1 1] 3,769,567 1 Oct. 30, 1973 Raver et al. 322/98 XArizienis et al... 322/28 Johnson 322/98 Ross 322/91 X PrimaryExaminer-J. D. Miller Assistant ExaminerRobert J. Hickey AttorneyW. F.Hyer et al;

ABSTRACT A generator battery charging system is disclosed in which ashunt load is periodically switched across the output of the generatorduring periods of low charging current requirements from the battery toprovide a substantially constant load on the generator.

13 Claims, 5 Drawing Figures VOLTAGE SENS/N6 AND SCI? CONTROL F-2/CIRCUITS l8 F/LTEP BATTERY m l BATTERY CHARGING SYSTEM This inventionrelates to apparatus for regulating the load on a prime mover drivengenerator being used to charge a battery.

In past battery charging systems where a prime mover driven generatorhas been the source of charging voltage, it has been customary toprovide voltage and/or current regulators which control the chargingvoltage and current to the battery. However, these regulators aredesigned to prevent excessive charging of the battery and not to providea substantially constant load for the prime mover.

This is particularly desirable where the generator is driven by a dieselengine, such as the case on many power systems used at remote,unattended locations, as on an offshore platform. A diesel engine whenoperating with a light load or a cycling load has the characteristic ofrunning too cool and/or operating with poor fuel combustion which cancause accelerated engine wear. Obviously such a situation is undesirablein the offshore application noted. Also, an unloaded condition on thegenerator can result in early failure of the generator.

As examples of the prior art, in each of'U. S. Pat. Nos. 1,762,297,1,834,280, and 1,162,027, a shunt resistor is provided to shunt theoutput of the generator when the generator voltage exceeds apredetermined amount. In these prior apparatus, the shunt load is fixedand connected to the generator only during extreme battery conditions,such as battery failure, and there is no provision for regulating theamount of the shunt load in relation to the battery load to provide asubstantially constant load to the generator, and thus the prime mover,irrespective of battery condition. Also, mechanical switches or relaysare used in these apparatus which are unsuitable for use in longunattended service in adverse environments.

In U. S. Pat. No. 3,447,059, a variable shunt load is provided across abattery which diverts changing current from the battery during lowcharging current demand periods. However, this patent is not directed tomaintaining a substantially constant load on a prime mover drivengenerator and in fact, the shunt regulator is not adapted to be operableuntil the battery terminal voltage exceeds a preselected value above thepoint at which battery charge demand has lessened.

It is thus an object of this invention to provide a battery chargingsystem and regulation apparatus therefor utilizing a prime mover drivengenerator as a source of charging current, and in which a substantiallyconstant generator load is provided during varying conditions of batterycharge or ultimate load demand.

Another object of this invention is to provide such a system andapparatus in which a substantially constant charge voltage to thebattery is provided even during changing generator temperature or speedconditions.

Another object of this invention is to provide such apparatus which issolid state, of reasonably simple and inexpensive construction, and hasrelatively long life when used unattended at-adverse locations.

These and other objects of this invention, which will be apparent uponconsideration of the appended drawings and claims, and the followingdetailed description, are accomplished according to the illustratedembodiment of this invention by providing a variable shunt load across aprime mover driven generator providing an alternating current chargingvoltage. The time that the shunt is connected across the generator todraw current therefrom during each charging voltage cycle is controlledby a sensing circuit that is responsive to the voltage of a batterybeing charged, and the phase of the charging signal. When the batteryvoltage is high, and the charging or load current low, the shunt isconnected across the generator output early in each alternating currentcycle, and thus for substantially all 'of the voltage cycle, and arelatively large current is drawn by the shunt load. When batterycondition is poor or load demand high, the shunt load is connectedacross the generator later in the alternating current cycle, and thecurrent required is drawn by the battery instead of the shunt load. Theapparatus can be adjusted so that the charging voltage for the batteryis well regulated at a predetermined voltage, or between predeterminedlimits, and the load on the generator is substantially constant. Also,the regulation provided compensates for changes in generator outputvoltage due to temperature and/or engine speed changes.

In the drawings, wherein like reference numerals are used throughout todesignate like parts, and wherein a preferred embodiment of thisinvention is illustrated,

FIG. 1 is a partial schematic and block diagram of a voltage generatorcharging system utilizing this invention;

FIG. 2 is a graph illustrating the relationship between voltage andcurrent at the output of the generator of FIG. 1;

FIG. 3 is a graph showing the relationship between the battery chargingvoltage and battery voltage when battery voltage is relatively high;

FIG. 4 is a graph showing the relationship between the battery chargingvoltage and battery voltage when battery voltage is relatively low; and

FIG. 5 is a detailed schematic of a system such shown in FIG. 1.

Referring now to the drawings, in FIG. 1, a D.C. storage battery 10 isillustrated as being connected at its terminals 11 and 12 to a chargingsystem 13, and to a load L, such as offshore warning lights or foghorns. Charging system 13 includes a permanent magnet generator 14 whichisdriven by a prime mover, such as a diesel engine 15, and provides analternating current charging voltage at the output terminals 14A and14B. Means is connected to output terminals 14A and 148 for respondingto the alternating current voltage output of generator 14 to provide asuitable charging voltage to battery 10. In the preferred embodiment ofthis invention illustrated in FIG. 1, this means includes an isolationtransformer 16 connected at its primary across terminals 14A and 14B,diode rectifiers 17 connected to the secondary of transformer 16 toprovide a fullwave rectifier charging voltage for battery 10, and afilter circuit 18 connected between rectifiers I7 and battery 10 toprovide a filtered D.C. charging voltage for battery 10.

A shunt means if connected across terminals 14A and 14B and is adaptedto provide a variable load for generator I4.In the illustratedembodiment this shunt means includes a ballastresistor 19 connected onone side to terminal 148, and a SCR switch 20 connected by its powerelectrodes between the other side of resistor'l9 and terminal 14A. SCR20 is arranged to provide one state in which conduction of currentbetween terminal 14A and 14B and through resistor 19 is interrupted, anda second state in response to a trigger signected between battery andelectrode g and is responsive to the battery voltage to provide thetriggering signal, so that a substantially constant load is provided forgenerator 10 by balancing the load between resistor 19 and battery 10.

As hereafter explained in detail with reference to FIG. 5, circuit 21 isalso responsive to the phase of the alternating current output ofgenerator 14 so that the time that SCR 20 is in its conductivestate,permitting resistor 19 to draw current during each alternating currentcycle, is a function of the voltage on battery 10 and thus the currentdemand of load L.

FIGS. 2-4 illustrate the regulating function of system 13. In FIG. 2,the curved line 22 shows the relationship of voltage and current atoutput terminals 14A and 14B of generator 14, the dotted line 23represents a normal battery voltage condition for battery 10, and theintersection 22' of lines 22 and 23A represents a satisfactory currentlevel for maintaining generator 14 and motor operations efficiently. Theprime objective of the present invention is to maintain the generatorvoltage and current within a suitable range on curve 22 above and belowpoint 22', within which the required charging voltage is provided to thebattery when needed, and the load on the generator is maintained at asufficient level.

Generator 14 includes a permanent magnet rotor and is non-overloading sothat it can be operated to provide the voltage current relationshipillustrated at any point on curve 22. Of course, the available voltageand current will also be function of engine speed or temperature of thepermanent magnet so that a different voltage amperage curve 22 would beprovided for different engine speeds or operating temperatures. Withoutthe regulating function of this invention, when the battery voltage ishigh, substantially no load would be drawn from generator 14, and curve22 would be in the high voltage, low current end. However, because ofthe regulation provided by this invention, as illustrated by FIG. 2,when the battery charge requirements or load L requirements on generator14 are at a minimum, shunt resistor 19 will draw substantial current andthe generator voltage may be maintained at a point 24 on curve 22, belowvoltage line 23. However, when full battery charging current is requiredor load L'is turned on (such as by closing a switch SW connected betweenload L and battery 10), the current drawn by resistor 19 decreases to asmall value and the generator voltage rises to the level of a point 25on curve 22, above the voltage level 23. For purposes of this disclosureand description of this invention, the reference to maintaining asubstantially constant load on generator 14, or a well of the rectifiedcharging signal at the input of filter 18. In FIG. 3 the battery voltagerepresented by line 23 is relatively high and at a value indicating thatbattery condition is good, or load L is off. With these conditions,circuit 21 responds to the battery voltage to provide the trigger signalfor SCR 20 early in each half cycle of waveform 26, for example, atpoints 27, and current from generator 14 will be conducted throughresistor 19 for substantially all of the voltage cycle. When SCR 20 isturned on and current flows through its power electrodes, this currentflow latches the SCR in its conductive state until the current fallsbelow a predetermined value, such as occurs when the waveform 26 goes inthe negative direction. Since a higher current is thus drawn fromgenerator 14 because of the shunt load, lower charging voltage forbattery 10 is produced and no charging current is drawn by battery 10.However, when load Lis applied to battery 10, or the condition of thebattery is poor, so that the battery voltage represented by line 23 islowered, circuit 21 responds to the lower battery volage to provide thetrig ger signal later in each half cycle of -waveform 26, for example,at points 28 in FIG. 4, and current from generator 14 will be conductedthrough resistor 19 for only a short time in each half cycle. In thiscase, the current drawn by shunt resistor 19 will be low and thecharging voltage raised to a level sufficient to charge the battery.

Referring now to FIG. 5, preferred circuitry for controlling the turn-ontimes of'SCR 20 is shown. In this FIG., SCR 20 is replaced by twos SCRsnoted as SCR 1 and SCR 2, connected with opposite polarity across eachother so that one conducts negative going current of the alternatingcurrent changing signal, and the other conducts such positive goingcurrent. Their gate electrodes are connected to opposite sides of thesecondary of an isolation transformer T so that the triggering signalsto each SCR are out of phase and the correct SCR conducts during thecycle of corrent polarity. Transformer T is the output of sensingcircuit 21 which comprises transistors Q Q Q Q and Q and theirassociated components. Battery voltage on terminal 11 is sensed bycircuit 21 by conducting this voltage through'a diode CR a filter 30,which filters out load transients, and a variable resistor R to the baseof transistor 0,. Transistors Q and Q and their associated componentsform a'diffe'rence amplifier 32 and the base of transistor O isconnected to a source of reference voltage 31 provided by a zenor diodeCR Difference amplifier 31 responds to a difference in the voltages atthe bases of Q, and O to provide an output or error signal at thecollector of Q,.

A circuit means 33 is provided to provide the triggering signals for SCR1 and SCR 2, in accordance with the battery voltage and tinierelationships previously noted with respect to the description of FIG. 3and FIG. 4. Circuit means 33 is connected to the output of differenceamplifier 32 and is responsive thereto, and is also responsive to thephase of the alternating current charging voltage from generator 14.Circuit means 33 is illustrated in FIG. 5 as including transistor Q andits associated components, and unijunction transistor 0., and itsassociated components, including a storage capacitor C connected to thegate electrode of unijunctioniQ Circuit means 33 also includes atransformer T connected at its primary to the alternating current outputof generator 14, and a bridge rectifier BR connected to the secondary oftransformer, to provide by a diode CR at, for example, 19 volts. Thisrectified voltage is conducted through'a resistor R, to the base B, ofunijunction transistor Q so that the potential on this base fluctuatesin accordance with the voltage and phase of the alternating currentcharging signal from generator 14, and the operation of unijunction Q,is synchronized to the AC. charging voltage.

DC. voltage for circuits 3] and 33, such as at the collector oftransistors Q,, Q and Q and the emitter of transistor Q is provided byconducting voltage from junction 34 through a diode CR and filteringthis voltage with a capacitor C Capacitor C, is also connected to thecollector of transistor Q and the base of this transistor is connectedthrough resistor R to the collector of transistor Q,. Charging voltagefor capacitor C, is conducted through a resistor R,, connected betweenjunction 34 and the emitter of transistor Q and through transistor 0;,which functions as a series variable impedance controlled by the errorsignal at its base. Thus, the state of charge of capacitor C, isdependent on the state of conduction of transistor Q and the latter isdependent on the magnitude of the error signal from difference amplifier32. Unijunction transistor Q4 fires to provide a pulse P at its base Bas a function of the fluctuating voltage on base B, and the charge oncapacitor C,, so that the time that pulse P is provided during each halfcycle of the A.C. charging voltage is varied, dependent on the state ofcharge of capacitor C,.

Pulse P is conducted to the base ofva transistor Q which drives theprimary of transformer T, to provide triggering signals for staticswitches SCR 1 and SCR 2.

In operation, when battery is in a high state of charge, potentiometerR,, is adjusted so that transistor Q, will drive Q just to the point ofsaturation. At this point, the charge time of capacitor C, is veryshort, causing very little delay between the zero crossing of the inputA.C. charging voltage and the SCR trigger signal, such as shown in FIG.3. SCR 1 is triggered on the positive swing of the AC. charging voltageand SCR 2 is triggered on the negative swing of the A.C. chargingvoltage.

When load L is applied to battery 10, causing the battery voltage todrop, a small voltage change is sensed by the .differential amplifier 32and this difference is amplified to the base of transistor Q TransistorQ impedance is increased, which causes the charging time for capacitor Cto increase. This delays the firing of unijunction Q and thus thegeneration of the triggering signals for SCR 1 and SCR2, which causesthese SCRs to turn on later in each half cycle of the alternatingcurrent charging voltage, such as shown in FIG. 4. When battery 10 is ina low charge state or a heavy load is applied, it is preferred that theimpedance of transistor 0;, be increased to a value such that C, chargetime is approximately the same as one half of the generator chargingvoltage, so that the static switch is never turned on.

Thus, depending on the voltage of battery 10, the current drawn fromgenerator 14 from either the battery and its load, or by resistor 19, orby a combination of these, will be continuously and automaticallymaintained between limits 24 and 25 on curve 22, and at a safe andefficient level for operation of generator 14, engine 15, and battery10.

From the foregoing, it will be seen that this invention is one welladapted to attain all of the ends'and objects hereinabove set forth,together with other advantages which are obvious and which are inherentto the apparatus. 7

It will be understood that certain features and subcombinations are ofutility and may be employed without reference to other features andsubcombinations. This is contemplated by and is within the scope of theclaims.

As many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that all matterherein set forth or shown in the accompanying drawings is to beinterpreted as illustrative and not in a limiting sense.

The invention having been described, what is claimed is:

1. An apparatus for controlling the load on an engine controlledgenerator being used to charge a battery, comprising, in combination:means for responding to the output of such a generator to provide acharging voltage for such a battery; shunt means adapted to be connectedto the output of said generator and to provide a secondary load that canbe switched across said output during each cycle of said chargingvoltage; and sensing means adapted to be connected to said battery andconnected to said shunt means, said sensing means responding to acondition of said battery to control said shunt means to automaticallyvary the time that said secondary load is connected to said output ofsaid generator during each cycle of said charging voltage to provide asubstantially constant load for said generator and said engine duringconditions of varying battery charge load on said generator.

2. The apparatus of claim 1 wherein the output of said generator is analternating current voltage and said shunt means includes a ballast loadand a switch means connected to said ballast load and switchable inresponse to a trigger signal between a first state in which current fromsaid generator is conducted through said ballast load, and a secondstate in which said conduction of current is interrupted, and saidsensing means provides such a triggering signal in response to the phaseof said alternating current voltage and the condition of said battery.

3. The apparatus of claim 2 wherein said ballast load is a resistor andsaid switch means includes a first SCR connected to conduct changingcurrent through said resistor when said alternating current voltage ispositive, and a second SCR connected to conduct such current when saidalternating current voltage is negative.

4. The apparatus of claim 2 wherein said sensing means includes meansfor providing a reference voltage, means connected to said referencevoltage means for comparing the voltage of said battery with saidreference voltage to provide an error signal in response to a differencein said compared voltages, and trigger signal producing means responsiveto the magnitude of said error signal and the phase of said alternatingcurrent voltage to provide said trigger signal.

5. The apparatus of claim 3 wherein said sensing means includes meansfor providing a reference voltage, means connected to said referencevoltage means for comparing the voltage of said battery with saidreference voltage to provide an error signal in response to a differencein said compared voltages, and trigger signal producing means responsiveto the magnitude of said error signal and the phase of said alternatingcurrent voltage to provide said trigger signal.

6. The apparatus of claim 4 wherein said trigger signal producing meansincludes a unijunction transistor connected at one of its baseelectrodes to be responsive to the phase of said alternating currentsignal, and a storage capacitor connected to the gate electrode of saidunijunction transistor and responsive to the magnitude of said errorsignal to control the firing of said unijunction transistor. 4

7. The apparatus of claim 5 wherein said trigger signal producing meansincludes a unijunction transistor connected at one of its baseelectrodes to be responsive to the phase of said alternating currentsignal, and a storage capacitor connected to the gate electrode of saidunijunction transistor and responsive to the magnitude of said errorsignal to control the firing of said unijunction transistor.

8. A system for supplying battery power comprising, in combination: abattery; a prime mover driven generator providing an alternating currentvoltage; means connected between said battery and said generator andresponding to said alternating current voltage to provide a chargingvoltage for said battery; a variable shunt regulator connected to shuntthe alternating current output of said generator; and sensing meansconnected to said battery and said shunt regulator and responsive to acondition of said battery to control said shunt regulator to balance thecurrent drawn from said generator between said battery and said shuntregulator during each cycle of said charging voltage to provide asubstantially constant load to said generator.

9. The system of claim 8 wherein said generator includes a permanentmagnet rotor.

10. The apparatus of claim 8 wherein said shunt regulator includes aballast load and a switch means connected to said ballast load andswitchable in response to'a trigger signal between a first state inwhich current from said generator is conducted through said ballastload, and a second state in which said conduction of current isinterrupted, and said sensing means provides such a triggering signal inresponse to the phase of said alternating current voltage and thecondition of said battery.

11. The apparatus of claim 10 wherein said ballast load is a resistorand said switch means includes a first SCR connected to conduct changingcurrent through said resistor when said alternating current voltage ispositive, and a second SCR connected to conduct such current when saidalternating current voltage is negative.

12. The apparatus of claim 10 wherein said sensing means includes meansfor providing a reference voltage, means connected to said referencevoltage means for comparing the voltage of said battery with saidreference voltage to provide an error signal in response to a differencein said compared voltages, and trigger signal producing means responsiveto the magnitude of said error signal and the phase of said alternatingcurrent voltage to provide said trigger signal.

13. The apparatus of claim 8 wherein said generator is driven by adiesel engine.

1. An apparatus for controlling the load on an engine controlledgenerator being used to charge a battery, comprising, in combination:means for responding tO the output of such a generator to provide acharging voltage for such a battery; shunt means adapted to be connectedto the output of said generator and to provide a secondary load that canbe switched across said output during each cycle of said chargingvoltage; and sensing means adapted to be connected to said battery andconnected to said shunt means, said sensing means responding to acondition of said battery to control said shunt means to automaticallyvary the time that said secondary load is connected to said output ofsaid generator during each cycle of said charging voltage to provide asubstantially constant load for said generator and said engine duringconditions of varying battery charge load on said generator.
 2. Theapparatus of claim 1 wherein the output of said generator is analternating current voltage and said shunt means includes a ballast loadand a switch means connected to said ballast load and switchable inresponse to a trigger signal between a first state in which current fromsaid generator is conducted through said ballast load, and a secondstate in which said conduction of current is interrupted, and saidsensing means provides such a triggering signal in response to the phaseof said alternating current voltage and the condition of said battery.3. The apparatus of claim 2 wherein said ballast load is a resistor andsaid switch means includes a first SCR connected to conduct changingcurrent through said resistor when said alternating current voltage ispositive, and a second SCR connected to conduct such current when saidalternating current voltage is negative.
 4. The apparatus of claim 2wherein said sensing means includes means for providing a referencevoltage, means connected to said reference voltage means for comparingthe voltage of said battery with said reference voltage to provide anerror signal in response to a difference in said compared voltages, andtrigger signal producing means responsive to the magnitude of said errorsignal and the phase of said alternating current voltage to provide saidtrigger signal.
 5. The apparatus of claim 3 wherein said sensing meansincludes means for providing a reference voltage, means connected tosaid reference voltage means for comparing the voltage of said batterywith said reference voltage to provide an error signal in response to adifference in said compared voltages, and trigger signal producing meansresponsive to the magnitude of said error signal and the phase of saidalternating current voltage to provide said trigger signal.
 6. Theapparatus of claim 4 wherein said trigger signal producing meansincludes a unijunction transistor connected at one of its baseelectrodes to be responsive to the phase of said alternating currentsignal, and a storage capacitor connected to the gate electrode of saidunijunction transistor and responsive to the magnitude of said errorsignal to control the firing of said unijunction transistor.
 7. Theapparatus of claim 5 wherein said trigger signal producing meansincludes a unijunction transistor connected at one of its baseelectrodes to be responsive to the phase of said alternating currentsignal, and a storage capacitor connected to the gate electrode of saidunijunction transistor and responsive to the magnitude of said errorsignal to control the firing of said unijunction transistor.
 8. A systemfor supplying battery power comprising, in combination: a battery; aprime mover driven generator providing an alternating current voltage;means connected between said battery and said generator and respondingto said alternating current voltage to provide a charging voltage forsaid battery; a variable shunt regulator connected to shunt thealternating current output of said generator; and sensing meansconnected to said battery and said shunt regulator and responsive to acondition of said battery to control said shunt regulator to balance thecurrent drawn from said generator between said battery and said shuntregulator during each cycle of said charging voltage to provide asubstantially constant load to said generator.
 9. The system of claim 8wherein said generator includes a permanent magnet rotor.
 10. Theapparatus of claim 8 wherein said shunt regulator includes a ballastload and a switch means connected to said ballast load and switchable inresponse to a trigger signal between a first state in which current fromsaid generator is conducted through said ballast load, and a secondstate in which said conduction of current is interrupted, and saidsensing means provides such a triggering signal in response to the phaseof said alternating current voltage and the condition of said battery.11. The apparatus of claim 10 wherein said ballast load is a resistorand said switch means includes a first SCR connected to conduct changingcurrent through said resistor when said alternating current voltage ispositive, and a second SCR connected to conduct such current when saidalternating current voltage is negative.
 12. The apparatus of claim 10wherein said sensing means includes means for providing a referencevoltage, means connected to said reference voltage means for comparingthe voltage of said battery with said reference voltage to provide anerror signal in response to a difference in said compared voltages, andtrigger signal producing means responsive to the magnitude of said errorsignal and the phase of said alternating current voltage to provide saidtrigger signal.
 13. The apparatus of claim 8 wherein said generator isdriven by a diesel engine.